Comment 1 for bug 1646049

Hello Jason: Could you check the setting "org.pantheon.files.preferences.show-remote-thumbnails"? This should allow thumbnailing of jpeg over smb (and ftp but not video files). At the moment this setting defaults to "false".

If you right-click on a remote folder you should get a "show remote thumbnail" entry in the context menu if you have a recent enough Files version.